Most of the presently available reciprocating pneumatically driven hand tools, such as saber saws, sanders, etc., are driven by means of air-actuated pistons. Although in many cases such drive systems are entirely satisfactory for the operation to be accomplished, they are generally unsuitable when the tool is to be utilized in a "heavy duty" application, such as in a professional shop.
When a heavy load is placed upon a piston-driven tool, such as by passing down hard on a reciprocating sander, the resistance to reciprocation is transmitted back to the piston and its throw and/or speed or travel is reduced accordingly.
Since the effectiveness of most reciprocating hand tools such as saws and sanders is measured by the distance that the material-working tool element travels per unit of time, i.e., the number of sawteeth which cross the line of cutting or the square inches of sandpaper which cross any arbitrary line on the material being sanded, it is quite apparent to those skilled in the art that the reduction of piston throw in such tools adversely affects the efficiency of the tool. As a result, the time and effort required to accomplish any specified operation with such a tool is increased more and more as greater force is exerted on the tool to press it against the workpiece. Although an optimum level of force versus time may be achieved, it is quite clear that if that optimum level is exceeded, the excessive force must be applied over a greater length of time in order to accomplish a desired result.
In the past, it has been believed to be impractical to drive such tools with rotary motors for two reasons. First, it has been thought that relatively complex linkages must be developed to convert the rotary motion into reciprocal motion. Secondly, reciprocation of the tool element per se generates dynamic forces during operation of the tool which, in the past, have been very suitably counteracted by the inertial weight and force of the reciprocating piston. In other words, the prior art machines have been developed in such a way that the piston weight would approximately equal the weight of the reciprocating tool element. The tool element is then connected to the piston by a linkage which causes the tool element to reciprocate in the opposite direction as the piston element, at any given instant.
Since pneumatically driven piston-actuated reciprocating tools thus are adversely affected by the imposition of a load thereon, such tools have failed to achieve a widespread usage as might otherwise be expected utilizing a power source as efficient as compressed air.
Pneumatically driven tools are not subject, under normal circumstances, to the generation of electrical potential between the tool body or housing and the surface upon which an operator is standing. As a result of this advantage of pneumatic tools, it is desirable to produce a pneumatically operated tool which is not subject to efficiency reduction as a result of a diminished throw of a piston when a load is placed on the tool.